Copper-electroplating baths



3,000,800 COPPER-'ELECTROPLATING BATHS Wennemar Strauss and Hans Wedell, both of Dusseldorf- Holthausen, Germany, assignors t Dehydag, Deutsche Hydrierwerke G.m.b.H., Dusseldorf, Germany, a corporation of Germany N0 Drawing. Filed Apr. 14, 1958, Ser. No. 728,033

Claims priority, application Germany Apr. 16, 1957 14 Claims. (Cl. 204-52) This invention relates to an electroplating process and the bath for the process. It more particularly relates to a process for obtaining bright, smooth electroplates of copper involving the addition of alkyl and aryl derivatives of thiourea to the copperplating bath.

It is well known in the art to add brightening agents to electroplating baths, such as copperand nickelplating baths, in order to improve the brightness properties of the deposited electroplates. It is further known that, in addition to the brightening agents, smoothing agents must also be added to the baths in order to provide a means for equalizing the unevenness produced by the roughness of the metal base.

It is an object of this invention to provide a process and a bath for the production of smooth, bright electrodeposits.

A further object is to provide a new smoothing agent for electroplating baths.

Another object is to provide a process for the electrodeposition of metals wherein the surface of the deposited metal is free from irregularities of the rough base metal on which the electrodeposit is made.

A further object is to provide a process for obtaining smooth, bright copper electrodeposits by adding alkyl and aryl derivatives of thiourea to a bright copper plating bath.

These and other objects of our invention will become apparent as the description thereof proceeds.

We have now found that thiourea derivatives which contain one or more alkyl or aryl radicals in the molecule produce a particularly good smoothing effect, if they are used in copper-electroplating baths together with certain groups of high quality brightening agents and, if desired, together with additional bath additives, such as additives for increasing ductility, wetting agents, and other such additives.

In accordance with our invention, such thiourea derivatives are used in copper-electroplating baths together with those high quality brightening agents which are characterized by one or more carbon atoms linked only to heteroatoms, the carbon atoms in turn being linked through a sulfur atom to a short aliphatic radical which carries a sulfonic acid group or another water-solubilizing group. Examples of such high quality brightening agents are the water-soluble salts of N,N-dimethyl-dithiocarbamic acid-n-propylester-w-sulfonic acid, N,N- diethyl-dithiocarbamic acidethylester-w-sulfonic acid, N,N pentamethylene dithiocarbamic acid n propylester-w-sulfonic acid, N,N-diethylamino-dithiocarbamic acid S propanediol-2,3,N butyl dithiocarbamic acid-N,S-bis-propane-w-su1fonic acid, dithiocarbamic acid-S-methylester-N-ethyl-N-butyl-w-sulfonic acid, 1,3,5- triazine 2,4,6 trimercapto 2 hydroxypropane sulfonic acid, 1,3,5-triazine2,4,-trimercaptoethane-sulfonic acid and other high quality brightening agents of similar structure, such as those which are described in French Patent No. 1,097,123, Belgian Patent No. 543,413 and Belgian Patent No. 540,564, or which are the subject matter of copending application Serial No. 618,183, new Patent No. 2,849,352.

The alkyl or aryl radicals in the thiourea derivatives may be attached to the nitrogen atom as Well as to the wherein R R R and R are selected from the group consisting of hydrogen, alkyl, aryl, aralkyl, cycloalkyl, hydroxyalkyl, hydroxyaryl, and hydroxy alkoxyalkyl radicals, at least one of the R through R, not being hydrogen.

Examples of suitable thiourea derivatives are the following: Naryl-N'-alkyl-thiourea, N-aralkyl-N'-a1kylthiourea, N-cycloalkyl-N'-alkyl-thiourea, Nalky1-N'- alkyl-thiourea, as well as S-alkyl-thiourea or their 7N- alkyl-substitution products. The alkyl radicals are primarily short-chain radicals with a maximum of about six carbon atoms. Examples of oxygen-containing alkylthiourea derivatives are the following: N-phenyl-N-oxethyl-thiourea, N-cyclohexyl-N'-oxethyl-thiourea, N-alkyl N-hydroXymethyl-thiourea, N-alkyl-N'-oxethyl-thiourea, N-phenyl -N- oxethyl-thiourea, N-phenyl -N'- hydroxypropyl-thiourea, N-phenyl-N-fl-(hydroxyethoxy)-ethylthiourea, N-benzyl-N'-hydroxyethyl-thiourea, N-4-hydroxyphenyl-N-hydroxyethyl-thiourea, and the like.

The simultaneous use of the thiourea derivatives with the above-described high quality brightening agents may also be applied especially in the process for direct electroplating of non-precious metals, in accordance with French Patent No. 1,127,418. In accordance with this process, firmly adhering copper-electroplates may be applied to non-precious metals, such as iron, without a preliminary cyanide copperplate by pretreating the metal objects to be copper-plated in an acid pickling bath containing inhibitors having a high inhibiting effect, and thereafter immediately and without intermediate rinsing copper-plating the object in an acid copper-plating bath.

The simultaneous use of these agents makes it possible to achieve especially high-grade copper-plates which are cpmpletely smooth and which are mirror-bright and require no subsequent treatment, such as polishing.

It has further been found to be advantageous to add to the baths containing the above agents certain organic amino compounds free from carboxyl groups, in order to improve the ductility of the copper-electroplates deposited therefrom. The addition of these organic amino compounds further achieves the result that inorganic impurities, such as those which are present, for example, as hardness components in water or in metal salts'of technical grade, do not exert a detrimental effect upon the properties of the copper-plates, which sometimes occurs inconjunction with the use of high-grade brightening agents of the type above described. Effective agents for increasing the ductility which meet these requirements are amino compounds, such as LB-propylenediamine, 1,3-bis-(diethylamino)-propanol-2, N,N,N,N- tetrabutyl 1,3 diaminopropanol 2, N,N,N,N' tetraethyl-l,3-diaminopropanol-2, or other sulfonic acid or sulfuric acid ester derivatives which contain one or more sulfonic acid groups or sulfuric acid ester groups. The use of compounds of this type is described in French Patent No. 1,118,019 and is the subject matter of copending application Serial No. 714,687.

Additional agents for increasing the ductility include halogen-containing tertiary amino compounds free from carboxyl groups, such as 2-diethylarnino-ethylchlorided, 3 diethylamino 1 chloro propanol 2, 1 dioxethylamino-3-chloro-propanol-2, or the quaternary rearrangement products formed from these compounds which contain the halogen in ionogenic linkage. Such compounds are described in German Patent No. 934,508 as well as in Belgian Patent No. 540,855.

The combination according to the present invention is to be used primarily in acid copper-electroplating baths. The thiourea derivatives are used in quantities of about 0.005 to 2:0 gm./1iter of bath liquid. Otherwise, the baths are operated under the same concentration, temperature and current density conditions described in the above-mentioned patents.

It is known that thiourea and certain thiourea derivatives have been proposed as brightening agents for electroplating baths, especially for copper-electroplating baths. These agents exhibit only moderate brightening effects in comparison with the brightening agents used in accordance with the invention, so that there Was no reason to use them as additional agents for improving the brightness. Surprisingly, however, we have found that the claimed thiourea derivatives in combination with the claimed high quality brightening agents produce an entirely different efiect; namely, that they are especially effective smoothing agents. It produces a very substantial improvement of the baths which contain these high quality brightening agents.

The following examples will further illustrate our invention and enable others skilled in the art to understand it more completely. It will be understood, however, that the invention is not limited to these particular examples.

Example I An acid copper-plating bath which contained 180 gm./liter CUSO4.5H20, 60 gm./liter concentrated sulfuric acid and, as a brightening agent, 1 gm./liter N,N- diethyl dithiocarbamic acid ethylester w sodium sulfonate, as well as 0.8 gm./liter N,N,N,N-tetrabutyl- 1,3-diaminopropanol-2 was modified with 0:01 gm./liter N,N'-diethylthiourea. When unpolished brass strips were electroplated within a current density range from 1 to 6 amp./dm. in this bath, mirror-bright copper-electroplates were obtained. With electroplate thicknesses of 15 to p, unevenness of the order of magnitude of 3 to 5a was substantially completely smoothed over. Without the addition of 0.01 gm./liter diethyl-thiourea, the copper-electroplates were mirror-bright but no smoothing effeet was present.

Example 11 The acid copper bath of Example I was modified by dissolving therein 0.25 gm./ liter N,N-diethyl-dithiocarbamic acid propylester-w-sodium sulfonate as a brightening agent, and 2 gm./ liter of the quaternary rearrangement product of 3-diethyl-amino-1-ch1oro-propanol-2 and 0.005 to 0.01 gm./liter N-phenyl-N-oXethyl-thiourea as smoothing agents. Metal objects electroplated in this bath were provided with a full bright copper-electroplate which smoothed out the unevenness of the metal base.

Example III The copper bath of Example I was modified by dissolving therein 1.2 gm./ liter 1,3,5-tIiazine 2,4,6-trimercapto- Z-hydroxypropane-sodium sulfonate, 0.8 gm./liter N,N, N,N' tetra n butyl 1,3 diaminopropanol 2, 0.02

' gm./ liter N,N-diethyl-dithiocarbamic acid-ethylester-wsodium sulfonate, 2 gin/liter of an ethoxylated and partially sulfonated fatty alcohol as. wetting agents, and

4 0.01 gmJliter N,N'-dioxethy1-thiourea as smoothing agent. When rough brass strips were electroplated in this bath within a current density range of 0.5 to 8 amp/rim. and a temperature range of :15 to 35 C., they were provided with full bright copper-electroplates. If the unevenness is of the magnitude of 3 to 5n, the deposit of an electroplate of 15p. substantially completely smooths out the roughness. Without the addition of the thiourea derivative, no smoothing effect could be observed.

While we have disclosed various specific embodiments of our invention, it will be apparent to persons skilled in the art that the present invention is not limited thereto, and that various changes and modifications may be made without departing from the spirit of the invention or the scope of the following claims.

We claim:

1. A process for producing a smooth, bright copper electroplate on a rough surface metal base from acidic copper plating baths containing a sulfonic acid brightening agent having a carbon atom linked exclusively to heteroatoms, said carbon atom being further linked through a sulfur atom to a lower aliphatic chain which carries the sulfonic radical which comprises adding to said bath a derivative of thiourea as a smoothing agent of the formula wherein R R R and R are selected from the group consisting of hydrogen, alkyl, aryl, aralkyl, cycloalkyl, hydroxyalkyl, hydroxyaryl, and hydroxyalkoxyalkyl radicals, at least one of R through R not being hydrogen, said smoothing agent being added in suflicient amount to efiect said smoothing of the copper plate.

2. The process of claim 1 wherein the thiourea derivative is N,N-diethyl thiourea.

3. The process of claim 1 wherein the thiourea derivative is N-phenyl-N'-oxethyl thiourea.

4. The process of claim 1 wherein the thiourea derivative is N,N-dioxethy1 thiourea.

5. The process of claim 1 wherein said smoothing agent is added in an amount of from about 0.005 to 2.0 gm./ liter of bath liquid.

6. A process for producing a smooth bright copper electroplate on a rough surface metal base from acidic copperplating baths containing a brightening agent having a carbon atom linked exclustively to heteroatoms, said carbon atom being further linked through a sulfur atom to a lower aliphatic chain which carries a Water solubilizing radical which comprises adding to said bath a derivative of thiourea as a smoothing agent of the formula wherein R R R and R are selected from the group consisting of hydrogen, alkyl, aryl, aralkyl, cycloalkyl, hydroxy-alkyl, hydroxyaryl, and hydroxyalkoxyalkyl radicals, at least one of R through R, not being hydrogen, said smoothing agent being added in sufficient amount to effect said smoothing of the copper plate.

7. The process of claim 6 wherein the water solubilizing radical is a sulfonic acid radical.

.8. An acidic copper electroplating bath for producing smooth, bright electrodeposits of copper on a rough surface metal base comprising an aqueous solution of an inorganic salt of copper, a sulfonic acid brightening agent having a carbon atom linked exclusively to heteroatoms, said carbon atom being further linked through a sulfur atom to a lower aliphatic chain which carries the s'ulfonic radical, and a derivative of thiourea as a smoothing agent of the formula.

wherein R R R and R are selected from the group consisting of hydrogen, alkyl, aryl, aralkyl, cycloalkyl, hydroxyalkyl, hydroxyaryl, and hydroxy alkoxyalkyl radicals, at least one of R through R, not being hydrogen, said smoothing agent being present in sufiicient amount to effect said smoothing of the electrodeposit.

9. The bath of claim 8 wherein the thiourea derivative is N,N-diethyl thiourea.

10. The bath of claim 8 wherein the thiourea derivative is N-phenyl-N-oxethyl thiourea.

11. The bath of claim 8 wherein the thiourea derivative is N,N'-dioxethy1 thiourea.

12. The bath of claim 8 wherein said smoothing agent is present in an amount of from about 0.005 to 2.0 gm./ liter of bath liquid.

13. An acidic copper electroplating bath for producing smooth, bright electrodeposits of copper on a rough surface metal base comprising an aqueous solution of an inorganic salt of copper, a brightening agent having a carbon atom linked exclusively to heteroatoms, said carbon atom being further linked through a sulfur atom to a lower aliphatic chain which carries a water solubilizing radical, and a derivative of thiourea as a smoothing agent of the formula References Cited in the file of this patent UNITED STATES PATENTS 2,563,360 Phillips et a1. Aug. 7, 1951 2,849,351 Gundel et a1 Aug. 26, 1958 2,849,352 Kirstahler et a1 Aug. 26, 1958 FOREIGN PATENTS 762,257 Great Britain Nov; 28, 1956 

1. A PROCESS FOR PRODUCING A SMOOTH, BRIGHT COPPER ELECTROPLATE ON A ROUGH SURFACE METAL BASE FROM ACIDIC COPPER PLATING BATHS CONTAINING A SULFONIC ACID BRIGHTENING AGENT HAVING A CARBON ATOM LINKED EXCLUSIVELY TO HETEROATOMS, SAID CARBON ATOM BEING FURTHER LINKED THROUGH A SULFUR ATOM TO A LOWER ALIPHATIC CHAIN WHICH CARRIES THE SULFONIC RADICAL WHICH COMPRISES ADDING TO SAID BATH A DERIVATIVE OF THIOUREA AS A SMOOTHING AGENT OF THE FORMULA 